Holographic magnifier

ABSTRACT

A magnifier constructed of a hologram having the characteristic that when a monochromatic light source, such as a television cathode-ray tube, is placed at a specified distance from the hologram, the television image as viewed through the hologram is magnified.

3 5 3 7 Z S R 7,? 1 OR 3.575.485 J W Rwy} [72] Inventor Lyman F. VanBuskirk OTHER REFERENCES Rldgecresucallfl Kock, PROC. OF THE lEEE, Vol.54, No. 11, Nov. 1966 [21] Appl. 789,094 pp. 1610-1612 (copy in 350/35)g d i 3 Kock a a1, lbid, pp. 1599-1601 (copy in 350/) 3 6 P Lei th eta1., JOURNAL OF THE OPTICAL SOCIETY OF [73] Assignee the United Statesof Amencaas represented AMERICA, VOL 57 Na 5 May 1967 699 (copy in bythe Secretary 0 the Navy 350 Schnar et a1. NATURE, Vol. 215, No. 5098,July 1967, pp. 541 HOLOGRAPHIC MAGNIFIER 2 Claims, 5 Drawing Figs.Primary Examiner-David Schonberg Assistant Examiner-Ronald .1. Stem [521U.S.Cl '85 Anomeys Edgar J Brewer and y Miner [51] Int. Cl ..G02b 27/00,

' G02b 5/18 FieldofSearch 350/35,

162 (P); 178/(lnqu1red), ABSTRACT: A magnifier constructed of a hologramhaving 56 R f Cted the characteristic that when a monochromatic lightsource, l e 1 such as a television cathode-ray tube, is placed at aspecified UNITED STATES PATENTS distance from the hologram, thetelevision image as viewed 3,405,614 10/1968 Lin et al 350/35 throu htheholo ram is ma ified.

PATENTED APR 20 l97| FIG. 1.

FIG. 4.

lNVIiNI'OR. LYMAN F. VANBUSKIRK BY FIG. 5.

ROY MILLER ATTORNEY.

HOLOGRAPIIIC mourn-"ran GOVERNMENT INTEREST The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

BACKGROUND OF THE INVENTION In certain applications it is desirable tomagnify the image appearing on a television cathode ray tube.Conventional magnification means, such as glass or plastic lenses, aretoo heavy and bulky in many cases. A magnifier constructed of a hologramwould be light and inexpensive to manufacture.

A typical hologram is created by exposing a high-resolution photographicplate, without camera or lenses. near a subject illuminated bymonochromatic spatially coherent light. A true three-dimensional imageof the subject is formed and may be viewed by illuminating the hologramwith a beam of monochromatic spatially coherent light. Such a typicalhologram, however, is not suitable for use as a holographic magnifier.

SUMMARY OF THE INVENTION In accordance with the present invention, ahologram is prepared by exposing a photographic plate with twomonochromatic spatially coherent light wave fronts. The first, orreference wave front, is a plane wave front which illuminates one sideof the photographic plate. A portion of the reference wave front issplit oh and by means of an optical fiber is caused to appear as a pointsource which illuminates a point on the other side of the photographicplate. When the first and second wave fronts simultaneously illuminateboth sides of the photographic plate, a fresnel diffraction pattern isformed. For each difi'erent point that the optical fiber illuminates, anew fresnel diffraction pattern is formed.

To make the hologram of the invention, a multiplicity of fresneldiffraction patterns are formed. When the resulting hologram isilluminated by monochromatic light, a point source at infinity for eachfresnel diffraction pattern will ap pear by wave front reconstructionwhen the hologram is viewed from the side opposite the monochromaticlight source.

A television cathode ray tube may be considered a source ofmonochromatic light for image reconstruction if the screen of thetelevision cathode-ray tube is placed at the same distance from thehologram as the optical fiber point source was'placed at the time thehologram was exposed. The sections of the television screen which emitlight will cause corresponding fresnel diffraction patterns to producepoint sources at infinity. When viewed from the side of the hologramopposite the side illuminated by the screen of the televisioncathode-ray tube, the reconstructed point sources will reproduce thepicture appearing on the screen of the cathoderay tube, and the picturewill appear magnified.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic of the apparatusused for making the hologram of the invention;

FIG. 2 is, a detail showing the interaction of spherical and plane wavefronts to form a fresnel diffraction pattern on a photographic plate toform a hologram;

FIG. 3 shows the fresnel diffraction pattern for a single point formedby the interaction of wave fronts as shown in FIG. 2;

FIG. 4 is a schematic of the hologram in use to enlarge the picture on atelevision screen; and

FIG. 5 is a ray diagram showing the hologram enlarging an Image.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, laser 10emits a plane wave front of monochromatic spatially coherent light I6which passes through beam splitter I5 and beam broadening optics 12 toilluminate one photosensitive side of photographic plate 13. A portionof plane wave front I6 is split off by beam splitter 15 and channeledinto optical fiber II. The optical fiber carries the split ofi portionof plane wave front I6 to a point on plane I4 which is located distanced away from the photosensitive side of photographic plate I3 oppositethe side illuminated by plane wave front I6. The monochromatic spatiallycoherent light emanating from the end of optical fiber II approximates apoint source because of the small diameter of the optical fiber.

The end of optical fiber II at plane 14 is capable of movement withinthat plane in directions x and y. Laser I0 and beam broadening optics 12are also capable of movement so that beam 16 moves through angles and IThe end of optical fiber II makes a raster scan. Its position withinplane 14 changes in a timed relationship with the angle at which planewave front I6 impinges upon photographic plate I3. As the end of opticalfiber 11 moves from the top to the bottom of plane 14, the angle atwhich plane wavefront I6 impinges upon photographic plate I3 angularlyvaries as a I function of 9. Similarly, as the end of optical fiber 11moves horizontally within plane 14, wave front I6 moves in a timedrelationship along angular path 1 Laser I0 is pulsed to obtain separateexposures while the end of optical fiber 11 scans plane I4 and planewave front 16 rotates along paths 9 and I The movement of optical fiberI0 and wave front 16 may be in steps or slowly continuous, since ineither case sharp separate exposures will result.

The purpose of the movement is to obtain numerous exposures at variousangles of incidence such that each point illuminated on the face of acathode-ray tube will produce a plane wave (emanating from the hologram)at the same angle to the hologram as plane wave 16 was for a similarlypositioned point source. That is, in utilizing the hologram theconstruction process is approximately reversed. An illuminated point onthe CRT replaces the point source. The angle between the hologram andthe plane wave remains the same for that particular point. The planewave, from the hologram.

FIG. 2 shows the interaction between spherical wave front I8 produced bythe light emanating from the end of optical fiber II and plane wavefront 16 emanating from laser 10 to form fresnel diffraction pattern 19shown in FIG. 3. During the scanning cycle, a plurality of fresneldiffraction patterns are exposed on photographic plate 13.

At the end of the scanning cycle photographic plate 13 is developed toproduce a hologram.

Referring to FIG. 4, a television cathode-ray tube 15 is placed so thatthe face is parallel to and distance d away from hologram I3. Thecharacteristic light emitted from a television cathode-ray tube willapproximate a source of monochromatic light for a short distance. Thuswhen television cathoderay tube 15 is placed parallel to and nearhologram 13, the light emanating therefrom approximates many pointsources of monochromatic light. When viewed from the side of thehologram opposite that illuminated by the light from television cathoderay tube' 15, human eye 20 will perceive the image on television cathoderay tube 15 as being magnified.

FIG. 5 is a ray diagram showing hologram I3 enlarging an image 17. Arrow17 represents a figure on the face of television cathode-ray tube I5placed at distance d away from holographic plate 13. Arrow I7 iscomprised of many point sources each of which emanates a spherical wavefront. When however, is now emanating spherical wave fronts 18a and 18b,corresponding to points at Plane wave front 160 and plane wave front 16bcreate an enlarged arrow 17' at infinity by wave front reconstruction.Similarly, each point on the screen of television cathode-ray tube lwill produce a point source which will cause cor-- responding fresneldiffraction patterns located on hologram 13 to produce correspondingpoint images at infinity. When viewed from the side of hologram l3opposite the side illuminated by the screen of television cathode-raytube 15, the reconstructed point sources will reproduce correspondingplane wave fronts which will form a magnified image of the pictureappearing on the screen of television cathode-ray tube 15,

lclaim: l. A method of making a holographic magnifier comprising:splitting a plane wave front of monochromatic spatially coherent lightinto first and second plane wave fronts; directing the first plane wavefront towards a first photosensitive side of a photographic plate;converting the second plane wave front into a divergent spherical wavefront; directing the spherical wave front towards the otherphotosensitive side of the photographic plate, and periodically changingthe angle at which said spherical wavefront impinges on saidphotographic plate such that the origin of said spherical wavefrontscans a plane situated parallel to and at a fixed distance away fromsaid plate; the step of directing said first plane'at which said planewavefront impinges on said plate such that the direction of propagationof said plane wavefront is always normal to a sphere whose origin is atthe center of the photographic plate, each direction of said planewavefront corresponding to one angle at which said second wavefrontimpinges on said plate such that said plane wavefront makes a fixedminimum angle with respect to the plane of said plate when the origin ofsaid spherical wavefront is at I an end point of its scan in anydirection and is normal to said plate when the origin of said sphericalwavefront is normal to the center of said plate;

exposing said photographic plate to said plane and spherical wave frontsfor each corresponding position of said wavefronts to produce aplurality of latent fresnel diffraction patterns;

developing said photographic plate to produce said plurality of fresneldiffraction patterns;

whereby when said developed photographic plate is positioned parallel toand at said fixed distance away from the face of a cathode-ray tube, animage on said tube when viewed through said developed plate ismagnified.

2. The method of making a holographic magnifier as set forth in claim Iwherein the second plane wave front is converted into a spherical wavefront by:

channeling the second plane wave front into the entrance of an opticalfiber having a diameter small enough to convert the light exitingtherefrom into a point source producing a spherical wave front.

1. A method of making a holographic magnifier comprising: splitting aplane wave front of monochromatic spatially coherent light into firstand second plane wave fronts; directing the first plane wave fronttowards a first photosensitive side of a photographic plate; convertingthe second plane wave front into a divergent spherical wave front;directing the spherical wave front towards the other photosensitive sideof the photographic plate, and periodically changing the angle at whichsaid spherical wavefront impinges on said photographic plate such thatthe origin of said spherical wavefront scans a plane situated parallelto and at a fixed distance away from said plate; the step of directingsaid first plane at which said plane wavefront impinges on said platesuch that the direction of propagation of said plane wavefront is alwaysnormal to a sphere whose origin is at the center of the photographicplate, each direction of said plane wavefront corresponding to one angleat which said second wavefront impinges on said plate such that saidplane wavefront makes a fixed minimum angle with respect to the plane ofsaid plate when the origin of said spherical wavefront is at an endpoint of its scan in any direction and is normal to said plate when theorigin of said spherical wavefront is normal to the center of saidplate; exposing said photographic plate to said plane and spherical wavefronts for each corresponding position of said wavefronts to produce aplurality of latent fresnel diffraction patterns; developing saidphotographic plate to produce said plurality of fresnel diffractionpatterns; whereby when said developed photographic plate is positionedparallel to and at said fixed distance away from the face of acathode-ray tube, an image on said tube when viewed through saiddeveloped plate is magnified.
 2. The method of making a holographicmagnifier as set forth in claim 1 wherein the second plane wave front isconverted into a spherical wave front by: channeling the second planewave front into the entrance of an optical fiber having a diameter smallenough to convert the light exiting therefrom into a point sourceproducing a spherical wave front.